Penam derivatives

ABSTRACT

Described is a novel process for the preparation of penams and penems useful as antibacterial agents, which comprises the reaction of an appropriate f-substituted-azetidin-2-one with a base, followed by reaction of the thereby formed penam compound with an oxidating agent and an organic or inorganic base. 
     Also described are novel pemam compounds useful as antibacterials which are prepared by the described process.

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 645,289, filled Aug. 29, 1984 now U.S. Pat. No.4,663,451.

SUMMARY OF THE INVENTION

This invention relates to a novel process useful in the synthesis ofpenems and penams having antibacterial activity and to novel compoundsproduced thereby.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

More particularly, this invention relates to a process for preparingcompounds of the following formula (I): ##STR1## in which R represents ahydrogen atom, a lower akyl, 2,2,2-trichloroethyl, acetonyl, allyl,benzyl, p-nitrobenzyl, p-methoxybenzyl, phenyl, o-nitrophenyl,benzhydryl or 1-phenoxyethyl group or a residue known to be hydrolysed"in vivo" and having favorable pharmacokinetic properties such as anacetoxymethyl, pivaloyloxymethyl or phthalidyl group or a group of theformula ##STR2## in which R₂ represents an alkyl group having from 1 to5 carbon atoms or an aryl group; R₁ represents a hydrogen atom, a loweralkyl, lower alkoxy, C₄ -C₆ cycloalkyl, or hydroxyalkyl group,preferably a hydroxy substituted lower alkyl group such as1-hydroxyethyl, the alcoholic function of the hydroxyalkyl group beingfree or protected, the protecting group (PG) preferably being ap-nitrobenzyloxycarbonyl, dimethyl-t-butylsilyl, diphenyl-t-butylsilyl,2,2,2-trichloroethoxycarbonyl, trimethylsilyl, benzyl, p-bromophenacyl,triphenylmethyl or pyranyl group, and Y represents:

(a) a hydroxymethyl group,

(b) ##STR3## wherein R₃ is hydrogen atom, lower alkyl, aralkyl, aryl,heteroalkyl, alkenyl or alkynyl of 2-6 carbon atoms, cycloalkyl of 4-6carbon atoms, optionally substituted by hydroxy, thiol, alkylthio, loweralkyl, lower alkoxy, halogen, cyano, carboxy, nitro, amino, amino loweralkyl or halo lower alkyl and Z is oxygen or sulphur atom;

(c) ##STR4## wherein R₄, R₅ represent independently hydrogen atom, loweralkyl, carbamoyl, lower alkanoyl, lower alkoxycarbonyl, amidinooptionally substituted by lower alkyl and Z is as above defined;

(d) ##STR5## wherein R₃ is as defined above and R₆ represents hydrogenatom, lower alkyl, carbamoyl, lower alkanoyl, hydroxy, lower alkoxy oraryloxy group;

(e) cyano group

(f) --CH₂ --X, wherein X represents

(i) NO₂ as such or as its nitronates of formula ##STR6## wherein R₇ isan alkaline metal cation, a hydrogen atom, a lower alkyl, aryl, alkenylor alkynyl of 2-6 carbon atoms, cycloalkyl of 4-6 carbon atoms,heteroaryl, lower alkanoyl or carbamoyl group;

(ii) --NR₄ R₅ wherein R₄, R₅ are as above defined;

(iii) ##STR7## wherein R₃, Z are as above defined;

(iv) ##STR8## wherein Z, R₄ and R₅ are as above defined; (v) --S(O)_(n)R₃ wherein R₃ is as defined above and n=0, 1, 2;

(vi) cyano group or

(vii) heteroarylthio group optionally saturated,

(viii) --OR₈, wherein R₈ is lower alkyl, carbamoyl, alkanoyl, C₅ -C₇cycloalkylcarbonyl or arylcarbonyl group.

Compounds of formula I wherein the O-protecting and N-protecting groupshave been removed are useful as antibiotics, being active against bothGram-positive and Gram negative strains.

The lower alkyl groups referred to above for R, R₁, R₃, R₄, R₅, R₆, R₇and R₈ contain 1 to 6 carbon atoms and are exemplified by methyl, ethyl,propyl, butyl, pentyl, hexyl and the corresponding branched chainisomers thereof.

The term "aryl" as used herein for R₁, R₂, R₃, R₆, R₇ and R₈ refers tophenyl, optionally substituted by lower alkyl, lower alkoxy and halogenatoms, e.g. p-tolyl, o-tolyl, m-tolyl, p-chlorophenyl, o-methoxyphenyl,etc.

Halogen atoms refer to a fluorine, chlorine, bromine or iodinesubstituents.

The term "heteroaryl" as used herein for R₃, R₇ and X (vii) refers toaryl groups having 1 to 4 heteroatoms in the ring such as pyridyl,furanyl, thienyl, thiazolyl, imidazolyl, tetrazolyl or the like. Theheteroaryl group may be optionally substituted by 1 to 3 lower alkylsubstituents, e.g. 2-methylpyridyl, 3-methylthienyl, 1-methyltetrazolyl,etc.

Where there is a possibility of the various position isomers, the term"heteroaryl" is intended to cover all the isomers, e.g. 2-pyridyl,3-pyridyl and 4-pyridyl.

The term "aralkyl" denotes lower alkyl groups substituted by one or morearyl groups such as benzyl, phenethyl, benzhydryl and the like. Thelower alkanoyl groups referred to above for R₄, R₅, R₆, R₇ and R₈contain 1 to 6 carbon atoms and are exemplified by formyl, acetyl,propionyl and butyryl.

The term alkaline metal cation denotes lithium, potassium and sodiumcations.

Compounds of formula I wherein Y represents a group of formula (b) to(f) as defined above are known as antibacterial agents being describedfor example in European Published Applications Nos. 2210 and 3960, andin British Patent Specification Nos. 2043639 and 2042515.

Additionally, penems of formula I wherein Y is a hydroxymethyl group areuseful intermediates for the preparation of useful antibiotics, asdescribed for example in our UK Patent Applications Nos. 2,111,496 and2,118,181.

Included within our inventive concept are also new penam compounds ofthe following formula IV ##STR9## wherein R, R₁, R₃ and Y are as abovedefined and n is 0, 1, 2. The compounds (IV) and compounds (IV) in whichat least one of, and possibly all of the N- and/or O-protecting group(s)have been removed possess β-lactamase inhibiting activity. Compounds(IV) wherein the N- and O-protecting groups have been removed andreplaced by hydrogen exhibit antibacterial activity. Thus, anotheraspect of our invention includes within its scope (1) pharmaceuticalcomposition comprising an amount of at least one compound (IV) or atleast one compound (IV) in which at least one of, and possibly all ofthe N- and/or O-protecting group(s) have been removed, where the amountis effective for β-lactamase blocking activity in combination with apharmaceutically acceptable carrier or coating. The invention alsoincludes (2) pharmaceutical compositions comprising an antibacteriallyeffective amount of penam of formula IV wherein all O- and optionally,all N-protecting groups have been removed together with a compatible,pharmaceutically acceptable carrier or coating. Also included withinthis invention is the method of eliciting a β-lactamase blockingresponse in warm-blooded animals. Also included within the invention isa method of eliciting an antibacterial response in a warm-blooded animalhaving a susceptible bacterial infection which comprises administeringto said animal a non-toxic, antibacterially effective amount of acompound of formula IV wherein all O- and optionally N-protecting groupshave been removed. The dosage administered of the penams of thisinvention is dependent upon the age and weight of the animal speciesbeing treated, the mode of administration, and (1) the type and severityof β-lactamase blocking activity desired, or (2) the type and severityof bacterial infection being prevented or reduced. Typically, the dosageadministered in either application, per day, will be in the range of100-5000 mg with 500-1000 mg being preferred.

For oral administration, the β-lactamase blocking and/or antibacterialcompounds of this invention may be formulated in the form of tablets,capsules, elixirs or the like. Likewise, they may be admixed with animalfeed. They may also be applied topically in the form of ointments, bothhydrophylic and hydrophobic, in the form of lotions which may beaqueous, non-aqueous or of the emulsion type, or in the form of creams.

The compounds of formula IV wherein all O- and optionally, N-protectinggroups have been removed may be utilized in liquid form such assolutions, suspensions and the like for otic and optic use and may alsobe administered parenterally via intramuscular injection.

A preferred aspect of this invention is directed to compounds of formula(IV) and to a process for preparing compounds of formula I

wherein Y represents

(a)' a hydroxymethyl group

(b)' ##STR10## wherein R₃ is as defined above, (c)' ##STR11## wherein R,R are each independently hydrogen atom, lower alkyl, carbamoyl or loweralkanoyl group;

(d)' ##STR12## wherein R₃ and R₆ are as defined above, (e)' a cyanogroup,

(f)' --CH₂ --X', wherein X' represents

(i) --NO₂ as such of as its nitronates of formula ##STR13## wherein R₇is as above defined; (ii)' --NR₄ R₅ wherein R₄, R₅ are eachindependently hydrogen atom, lower alkyl, carbamoyl or lower alkanoylgroup;

(iii)' ##STR14## wherein R₃ is as above defined; (iv)' ##STR15## whereinR₄ and R₅ are as defined above; (v)' --S(O)_(n) R₃, wherein R₃ is asdefined above

(viii)' --OR₈ wherein R₈ is as defined above.

Particularly preferred compouds prepared according to the process of thepresent invention are compounds of formula (I) or (IV) wherein R₁ is anα-hydroxyethyl group optionally protected and Y represents:

(a)" hydroxymethyl group

(b)" ##STR16## wherein R₃ is as defined above or (f)" --CH₂ --X",wherein X" represents

(i)" --NO₂ as such or as its nitronates of formula ##STR17## wherein R₇is as above defined; (ii)" --NR₄ R₅, wherein R₄, R₅ are as abovedefined;

(iii)" ##STR18## wherein R₃ is as defined above, (viii)" --OR₈, whereinR₈ is as above defined.

The compounds of formula (I) and (IV) possess several centers ofchirality, and the process of this invention provides compounds havingthe configuration at C₅ of the absolute stereochemistry R, the6-substituents may have either α or β orientation, α orientation beingpreferred.

The most preferred embodiment of this invention is a process directed tothe preparation of compounds of the following formula (I"B) having astereo configuration designated 5R, 6S, 8R and having the followingrepresentative spatial configuration: ##STR19## wherein PG is anO-protecting group and R is as defined above. The compounds of formula(I) are prepared by the process of this invention which comprises: (a)cyclizing an azetidinone (II): ##STR20## wherein R, R₁ and R₃ are asdefined above and E represents an electron withdrawing group selectedfrom heteroarylthio methyl, --NO₂, CN, ##STR21## S(O)_(n) R₃ groups,wherein R₃, Z and n are as above defined, in tetrahydrofuran, hexane ortoluene by treatment with a base at a temperature of from -100° to 0°C., (b) optionally converting if necessary the thereby produced penam offormula (III) ##STR22## wherein E, R, R₁ and R₃ are as defined above,into a penam of formula (IV) ##STR23## wherein R, R₁, R₃ and Y are asdefined above and (c) oxidizing and treating with a tertiary amine or analkaline metal carbonate the so produced compounds of formula (IV) or(III) in an inert solvent at a temperature of from 0° to 130° C., togive the desired compounds of formula (I), which may optionally beconverted into other compounds of formula (I) wherein Y is different. By"inert solvent" in step (c) is meant any organic or inorganic solvent inwhich the starting compound and reagent are soluble, and which will notinterfere with the process under the reaction conditions thereof, sothere are produced a minimum of competing side reactions. Inert solventwhich may be used in our process include aromatic hydrocarbons (e.g.benzene, toluene and the like), aliphatic ethers (e.g. diethyl ether,dipropyl ether), cyclic ethers (e.g. dioxane, tetrahydrofuran) and,preferably, halogenated hydrocarbons such as methylene chloride andchloroform.

In the first step (a) of the process, the bases which may be employedare preferably organometallic derivative such as LiN[Si(CH₃)₃ ]₂,##STR24## n-butyl Li, t-butyl Li, Me Li, phenyl Li and the like.

The oxydation of the step (c) may be carried out by convential oxydatingagents, such as peracids (e.g. metachloroperbenzoic, peracetic acid andthe like) or ozone. The tertiary amine is preferably triethylamine, ordi-isopropylethyl amine and the alkaline metal carbonate is preferablysodium bicarbonate.

The conversions under step (b) from compounds (III) or (I) torespectively compounds (IV) or (I) wherein Y is different may beperformed by well known literature methods.

For example, compounds (IV) or (I) wherein Y represents a group offormula CH₂ NR₄ R₅ wherein R₄ and R₅ are as defined above may berespectively obtained from compounds (III) or (I) wherein CH₂ E or Yrepresent a nitromethyl group by reduction (e.g. with H₂ in presence ofPd/C) and subsequent optimal alkylation or acylation.

Compounds (IV) or (I) wherein Y represents a formyl group may berespectively obtained from compounds (III) or (I) wherein CH₂ E or Yrepresent a nitromethyl group by basic treatment, optional quenchingwith an alkylating agent such as CH₃ I and subsequent ozonisation.Compounds (I) wherein Y represents a hydroxymethyl group may be obtainedfrom compounds (I) wherein Y represents a formyl group by reduction.Compounds (I) wherein Y represents a group of formula ##STR25## or CN,wherein R₃, R₄, R₅, and Z are as above defined may be obtained fromcompounds (I) wherein Y represents a formyl group by oxydation andsubsequent reactions well known to people skilled in the art.

A preferred embodiment of the process of the present invention is shownvia flow diagram as follows: ##STR26##

In carrying out this preferred mode of our inventive process, theazetidinzone of formula (II') [which is a compound of formula (II)wherein R₁ is a hydroxyethyl group protected by t-butyldimethylsilylgroup, R is p-nitrobenzyl, R₃ is a methyl group and E is a nitro group]having the stereoconfiguration 3S,4R,5R in a tetrahydrofuran solution isadded to a solution containing about 2 molar equivalents of LiN[Si(CH₃)₃ ]₂ at -78° C. After 10 minutes reaction time, the obtainedcompound of formula (III') is isolated and purified via chromatographyon silica gel and crystallization from diisopropyl ether. The compoundof formula (IV') [which is a compound of formula IV wherein Y representsa formyl group] is obtained by treating the compound (III') withLiN[Si(CH₃)₃ ]₂ in tetrahydrofuran at -78° C. for 10 minutes, followedby an addition of CH₃ I and subsequent ozonization. To the so producedpenam (IV') in a chloroform solution at 0° C. there is added about 1.05molar equivalents of metachloroperbenzoic acid in chloroform. After 10minutes reaction time, an excess of NaHCO₃ is added and the desiredpenam (I_(A) ') isolated and purified via chromatography on silica gel.

The conversion of compound (I_(A) ') to compound (I_(B) ') is carriedout by reaction with L-selectride in tetrahydrofuran at -78° C.

The starting intermediates (II) for the process of the present inventionare prepared according the following reaction scheme, wherein L is aleaving group such as acetoxy or a benzoate group, and R, R₁, R₃, E andY are as above defined. ##STR27## The route to compound (II) commencesfrom compounds V, known compounds or prepared by procedures known in theart

Compound V is condensed with a suitable dipotassium salt of generalformula ##STR28## already known in literature [e.g. Ber. 52, 542 (1919)]or prepared by analogous procedures, and then alkylated to give compound(VI). The subsequent conversion of compound (VI) in compound II may beperformed using well known methods.

The invention is illustrated by the following examples in which theabbreviations PNB for p-nitrobenzyl, and TBDMS for t-butyl-dimetylsilylare used.

PREPARATION A(3S,4R)-3[(1R)-tert-butyldimethylsilyloxyethyl]-4-[(1-methylthio-2-nitro)ethylenthio]azetidin-2-one

The solution of the dipotassium-2-nitroethylen dithiolate (1.1 g, 4.95mM) in ETOH (5 mL):water (5 ml) was dropped into a cooled (0° C.) andstirred solution of the4-acetoxy-3(R)-[(1R)-tert-butyldimethylsilyloxyethyl]azetidin-2-one(1.44 g, 5 mM) in ethanol (20 mL):water (5 mL).

The mixture was then stirred for a further 10 min. and dimethylsulfatewas added at 0° C.

The solution was then stirred over 1 hr at room temperature, cooledagain, water (50 mL) was added and the suspension was stirred for 30min. at 0°. The solid was collected by filtration; washed with smallportions of cold EtOH/H₂ O, collected and dissolved in Et₂ O. Theethereal solution was dried over anhydrous magnesium sulfate decolorizedwith charcoal, filtered and evaporated. The solid residue was thencrystallized from chloroform/hexanes to give the title compound as awhite-yellowish solid, 1.25 g (66%).

m.p. 144°-146° C. (dec).

[α]_(D) =+215.3 (c 1.55, CHCl).

I.R. (CHCl₃ film) cm⁻¹ : 3300, 1770, 1525.

NMR (90 MHz), CDCl₃) δ(ppm): 0.08 (3H, s); 0.09 (3H, s); 0.88 (9H, s);1.25 (3H, d, J=6.5 Hz); 2.62 (3H, s); 3.28 (1H, dd, J=2.6 and 3 Hz); 4.3(1H,, m); 5.44 (1H, d, J=2.6 Hz); 6.84 (1H, br s); 7.05 (1H, s).

Mass: CI: 379 (M+1), 228 (M-150).

C₁₄ H₂₆ N₂ O₄ Si requires: C 44.41; H 6.92; N 7.40; S 16.94. found: C44.53; H 7.00; N 7.32; S 16.61.

PREPARATION Bp-Nitrobenzyl{(3S)-[(1R)-tert-butyldimethylsilyloxyethyl]-(4R)-[(1-methylthio-2-nitro)ethylenthio]-2-oxoazetidin-1-yl}acetate

To a solution of(3S,4R)-3-[(1R)-tertbutyldimethylsilyloxyethyl]-4-[(1-methylthio-2-nitro)ethylenthyo]azetidin-2-one(1.51 g, 4 mM) in dry CH₂ Cl₂ (50 mL) at 0° C., were added CaCO₃ (2 g),p-nitrobenzyl chlorocarbonyl formate (1.2 g) and diisopropyl ethylamine(0.8 mL) in sequence. The mixture was filtered through celite, washedtwice with cold H₂ O, dried and evaporated in vacuo. The residue wastaken up with toluene and purified by a short column of silanized silicagel eluting with toluene -0.5% EtOAc to give 1.7 g of p-nitrobenzyl2-{(3S)-[(1R)-tert-butyldimethylsilyloxyethyl]-(4R)-[(1-methylthio-2-nitro)ethylenthio]-2-oxoazetidin-1-yl}-2-oxoacetate as a yellow syrup.

IR cm⁻¹ (CHCl₃) film; 1820, 1760, 1720, 1530.

NMR (CDCl₃) δ(ppm): 0.1 (6H, s); 0.9 (9H, s); 1.35 (3H, d, J=6.0 Hz);2.6 (3H, s); 3.5 (1H, dd); 4.4 (1H, m) 5.3 (2H, s); 6.2 (1H, d,, J=3.5Hz); 7.1 (1H, s); 7.6 (2H, d); 8.25 (2H, d).

The above syrup (1.7 g) was dissolved in CHCl₃ (20 mL) and treated withtrimethylphosphite (0.77 mL, 6.5 mM) at room temperature under Argon.The solution was then stirred 36 hours at room temperature. The crudeproduct was then purified by column chromatography yielding 1.55 g ofp-nitrobenzyl2{(3S)-[(1R)-tert-butyldimethylsilyloxyethyl]-(4R)-[(1-methylthio-2-nitro)ethylenthio]-2-oxoazetidin-1-yl}-2-trimethoxyphosphoranylidene acetate.

IR (CHCl₃ film) cm⁻¹ 1770, 1650, 1530.

The solution of the above phosphoranylidene acetate in THF (50 mL):water (10 mL) and p-toluen sulphonic acid (catalitic amount) was stirredat room temperature for 1 hr. The solution was then poured into 1% aq.NaHCO₃ and EtOAc. The organic phase was separated, washed twice withbrine, dried and evaporated. The crude residue was purified by columnchromatography to give the title compound as a yellow oil (0.82 g).

IR (CHCl₃, film), cm⁻¹, 1780, 1760 (sh), 1530.

NMR δ(ppm) 0.07 (3H, s); 0.09 (3H, s); 0.88 (9H, s); 1.28 (3H, d, J=0.6Hz); 2.48 (3H, s); 3.25 (1H, dd,, J=2.5, 4 Hz); 3.90, 4.09, 4.23, 4.45(ABq, 2H, J=19 Hz); 4.35 (1H, m); 5.25 (2H, s); 5.78 (1H, d, J=2.5 Hz);7.0 (1H, s); 7.55 (2H, d, J=8 Hz); 8.25 (2H, d, J=8 Hz).

Mass. spectral data: CI: 572 (M+1); 514 (M-C₄ H₉); 421 (M-150).

EXAMPLE 1p-Nitrobenzyl(5R,6S)-6-[(1R)tert-butyldimethylsilyloxyethyl]-2-methylthio-2-nitromethylpenam-3-carboxylate

To a solution of hexamethyldisilazane (337 μl, 1.60 mM) in dry TMF (10mL) at 0° C. under Argon was added a solution of n butyl lithium (1.6Msolution in n-hexane) dropwise and with stirring (1 mL, 1.6 mM). Theresulting colourless solution was stirred 30 minutes at 0° C. It wasthen cooled at -78° C. and a solution of p-nitrobenzyl{(3S)-[(1R)-tertbutyldimethylsilyloxyethyl]-(4R)-[(1-methylthio-2-nitro)ethylthio]-2-oxoazetidin-1-yl}acetate(430 mg, 0.75 mM) in TMF (5 mL) was added in 2 minutes.

The resulting dark red solution was stirred at -78° C. over 10 min. andquenched with water containing AcOH. The mixture was let warm to roomtemperature and then partitioned between EtOAc/H₂ O. The organic phasewas washed twice with salted water, dried, evaporated in vacuo andpurified by column chromatography to give the title compound as a waxysolid. It was then crystallized from diisopropyl ether (0.22 g, 51%).

mp 103°-105° C.

[α]_(D) =+216.9 (c 0.775 CHCl₃).

IR (CHCl₃, film) cm⁻¹ 1780, 1750, 1560, 1525.

NMR (60, 90, 400 MHz, CDCl₃) δ(ppm); 0.01 (6H, s); 0.09 (9H, s); 1.26(3H, d, J=6.3 Hz); 2.33 (3H, s); 3.39 (1H, dd, J=1.8 and 4.5 Hz); 4.15(1H, s); 4.28 (1H, m); 4.79, 4.82, 5.47, 5.50 (2H, ABq, J=13.4 Hz); 5.20(1H, d, J=1.8 Hz); 5.29, 5.32, 5.36, 5.39 (2H ABq, J=13 Hz); 7.65 (2H,d, J=9 Hz); 8.25 (2H, d, J=9 Hz).

Mass. DCI-HN₃ : 572 (M+1); 514 (M-C₄ H₉); 372 (M-199).

C₂₃ H₃₃ N₃ O₈ S₂ Si requires: C 48.31; H 5.82; N 7.35; S. 11.22. found:C 48.13; H 5.75; N 7.25; S 10,89.

EXAMPLE 2p-Nitrobenzyl(5R,6S)-6[(1R)-tert-butyldimethylsilyloxyethyl]-2-methylthio-2-formylpenam-3-carboxylateMethod A

To a solution of lithium hexamethyl disilylazide in TMF (5 mL) [preparedas in the preceding example from hexamethyldisilazane (32 μl, 0.15 mM)and n BuLi 1.6M solution in n hexane (95 μl 0.15 mM)] was added thesolution of the penam prepared in example 1, at -78° C. in 1 minuteunder Argon. The dark yellow mixture was stirred 10 min. at -78° C. andCH₃ I (200 μl) was added. After further 10 min. the mixture was ozonizedfor 15 min., monitoring the progress by TLC). The excess of ozone waspurged with argon and then dimethylsulfide was added (200 ul) togetherwith a few drops of acetic acid (in order to maintain the pH at about6). The reaction mixture was allowed to warm to 0° C. and then pouredimmediately in aqueous NaCl solution/ether. The ethereal phase waswashed twice with NaCl, dried over MgSO₄, evaporated in vacuo in thecold and purified by passing it rapidly through a column of silanizedsilica gel (eluting with toluene/7 hexane 3) to give the title compoundas colourless oil (45 mg).

IR (CHCl, film): cm⁻¹, 1785, 1750, 1725, 1525.

NMR (60, 90, 400 MHz, CDCl₃) δ(ppm) 0.05 (3H, s); 0.07 (3H, s); 0.86(9H, s); 1.23 (3H, d, J=6.3 Hz); 2.17 (3H, s); 3.40 (1H, dd, J=1.8 and4.1 Hz); 4.19 (1H, s); 4.25 (1H, m); 5.21 (1H, d, J=1.8 Hz); 5.23, 5.26,5.36, 5.39 (2H, ABq, J=13 Hz); 7.56 (2H, d, J=9 Hz); 8.21 (2H, d, J=9Hz); 9.21 (1H, s).

Mass DCI, isobutane: 483 (M-C₄ H₉); 341 (M-199).

Method B

To a solution of lithium hexamethyldisilylazide in TMF (10 mL) [preparedfrom hexamethyldisilazane (337 μL, 1.60 mM) and n BuLi 1.6M solution inn hexane (1 mL, 1.6 mM)] was added a solution ofp-nitrobenzyl{(3S)-[(1R)-tertbutyldimethylsilyloxyethyl]-(4R)-[(1-methylthio-2-nitro)ethylenthio]-2-oxoazetidin-1-ylacetate (430 mg, 0.75 mM) in TMF (5 mL) in 2 minutes. The resultingsolution was stirred 10' at -78° C. and CH₃ I (400 μl) was added.

After further 10 minutes the mixture was ozonized for 15 minutes. Afterwork-up as described in method A the title compound was obtained (0.11g) with chemical physical properties identical as in method A.

EXAMPLE 3p-Nitrobenzyl(5R,6S)-6[(1R)-tert-butyldimethylsilyloxyethyl]-2-formylpenem-3-carboxylate

To the stirred and cooled (0° C.) solution ofp-nitrobenzyl(5R,6S)-6[(1R)-tert-butyldimethylsilyloyethyl]-2-methylthio-2-formylpenam-3-carboxylate(54 mg, 0.1 mM) in chloroform (3 mL) was added a solution ofmetachloroperoxybenzoic acid (21.6 mg, 0.105 mM; 85%) in chloroform (1.5mL). After 10 minutes the solution was vigorously stirred with a NaHCO₃solution at 0° C. The aqueous phase was separated and the organic phasewas stirred vigorously for 30 minutes at room temperature with water.

The aqueous phase was discarded and the organic phase was dried overMgSO₄, filtered, washed carefully with chloroform and evaporatedrepeatedly in vacuo. The crude residue was purified by columnchromatography eluting with an EtOAc/hexanes gradient to give the titlecompound as an amorphous solid (26 mg).

IR (CHCl₃, film) cm⁻¹ : 1790, 1715, 1660, 1520.

NMR (CDCl₃) δ(ppm) 0.04 (3H, s); 0.08 (3H, s); 0.83 (9H, s); 1.25 (3H,d, J=6.3 Hz); 3.91 (1H, dd, J=2.0 and 3.3 Hz); 4.27 (1H, m); 5.30, 5.33,5.45, 5.49 (2H, Abq, J=13 Hz); 5.68 (1H, d, J=2.0 Hz); 7.63 (2H, d, J=9Hz); 8.23 (2H, d, J=9 Hz); 10.42 (1H, s).

Mass DCI-isobutane: 435 (M-C₄ H₉); 293 (M-199)

UV (CHCl₃) λmax (nm): 265, 390.

EXAMPLE 4p-Nitrobenzyl-(5R,6S)-6-[(1R)-tert-butyldimethylsilyloxyethyl]-2-nitromethylpenem-3-carboxylate

A solution of metachloroperoxybenzoic acid (85%, 0.105 mM, 21.5 mg) inchloroform (1.5 mL) was added to a stirred and cooled (0° C.) solutionofp-Nitrobenzyl-(5R,6S)-6/(1R)tertbutyldimethylsilyloxyethyl/-2-methylthio-2-nitromethylpenam-3-carboxylate(57.1 mg, 0.1 mM) in chloroform (3 mL).

After 10 minutes the solution was vigorously stirred with a NaHCO₃solution at 0° C. The aqueous phase was separated and the organic phasewas washed at room temperature with water. The collected organic phasewas dried over MgSO₄, filtered, and evaporated in vacuo yielding ayellowish oil (20 mg).

IR (CHCl₃) cm⁻¹ : 1795, 1715.

UV (CHCl₃) max nm: 264, 334.

NMR (CDCl₃) ppm; 0.01 (3H, s); 0.09 (3H, s); 0.9 (9H, s); 1.32 (3H, d,J=6 Hz), 3.95 (1H, dd, J=1.9 and 3.8 Hz); 4.3 (1H, m); 5.28, 5.35, 5.48and 5.55 (2H, ABq, J=13.8 Hz); 5.39, 5.47, 6.10 and 6.17 (2H, ABq, J=15Hz), 5.86 (1H, d, J=1.9 Hz) 7.6 (2H, d, J=9 Hz); 8.23 (2H, d, J=9 Hz).

Mass spectral data (FD): 523 (M), 466 (M-C₄ H₉).

EXAMPLE 5p-Nitrobenzyl(5R,6S)-6-[(1R)-tert-butyldimethylsilyloxyethyl]-2-hydroxymethylpenem-3-carboxylate

To a solution ofp-nitrobenzyl(5R,6S)-6[(1R)-tert-butyldimethylsilyloxyethyl]-2-formylpenem-3-carboxylate(49 mg, 0.1 mM) in THF (10 mL) was added L-selectride 1M solution (100μl, 0.1 mM) at -78° C. dropwise, under argon and with stirring.

The solution was stirred 5 min. at -78° C. and then quenched withammonium chloride solution at -78° C. (1 mL). The reaction mixture waswarmed to room temperature and then partitioned between EtOAc/H₂ O. Theaqueous phase was extracted twice with EtOAc and the combined organicextracts were washed twice with sodium chloride solution, dried oversodium sulfate, filtered, and evaporated in vacuo.

The crude was then purified by column chromatography yielding the titlecompound as an amorphous solid (31 mg).

UV (CHCl₃) λmax: 265, 324.

IR (CHCl₃, film) cm⁻¹ : 3400 (br), 1790, 1710, 1525.

NMR (400 MHz, CDCl₃) δ(ppm); 0.04 (3H, s); 0.08 (3H, s); 0.82 (2H, s);1.25 (3H, d, J=6.3 Hz); 3.32 (1H, brt, J=7.0 Hz); 3.77 (1H, dd, J=1.7and 3.8 Hz); 4.26 (1H, m); 4.71 (2H br m); 5.21, 5.25, 5.41, 5.44 (2H,ABq, J=13.7 Hz); 5.64 (1H, d, J=1.7 Hz); 7.62 (2H, d, J=8.7 Hz); 8.23(2H, d, J=8.7 Hz).

Mass spectral data: CI: 495 (M+1); 437 (M-C₄ H₉); 295 (M-199).

[α]_(D) (cl, CHCl₃)=+33.5°.

EXAMPLE 6p-Nitrobenzyl(5R,6S)-6-[(1R)-hydroxyethyl]-2-hydroxymethylpenem-3-carboxylate

To a solution ofp-nitrobenzyl(5R,6S)-2-hydroxymethyl-6-[(1R)-tert-butyldimethylsilyloxyethyl]penem-3-carboxylate(1.2 g, 2.4 mmol) in THF (50 ml), acetic acid (1.47 ml, 24 mmol) andtetrabutylammonium fluoride (2.27 g, 7.2 mmol) were added.

The resulting mixture was stirred at room temperature for 16 hours. Thesolution was then evaporated in vacuo and the residue waschromatographed on silica gel eluting with ethyl acetate/cyclohexanemixtures to give the title product as a light yellow solid (775 mg,85%).

UV (EtOH) λmax 264, 322.

NMR (Acetone) δppm (60 MHZ) 1.45 (3H, d, J=6.5 Hz); 3.67 (1H, dd, J=1.5,6.0 Hz); 4.10 (1H, m); 4.72 (2H, s); 5.32 (2H, ABq, J=14 Hz, separationof inner lines 8 Hz); 5.59 (1H, d, J=1.5 Hz); 7.69 (2H, d, J=7 Hz); 8.18(2H, d, J=7 Hz).

EXAMPLE 7Sodium(5R,6S)-6-[(1R)-hydroxyethyl]-2-hydroxymethylpenem-3-carboxylate

A solution ofp-nitrobenzyl(5R,6S)-6-[(1R)-hydroxyethyl]-2-hydroxymethyl-penem-3-carboxylate(450 mg. 1.2 mmol) in EtOAc (25 ml) containing NaHCO₃ (100 mg. 1.2 mmol)was hydrogenated over 5% Pd/C (450 mg) under normal pressure for 1 hour.A further amount of 5% Pd/C (750 mg) was then added and thehydrogenation was continued for 1 hour.

The mixture was then filtered and the organic phase was discarded. Theaqueous phase was concentrated in vacuo to give a brownish oil which waspurified on a reverse phase column eluting with water. The title productwas so obtained as an amorphous solid (210 mg 61.2%).

UV (H₂ O) λmax 259, 305 nm.

NMR (D₂ O) δppm (90 MHZ) 1.30 (3H, d, J=7 Hz); 3.88 (1H, dd, J=1 and 6.3Hz); 4.23 (1H, m); 4.63 (2H, ABq, J=14.5 HZ, separation of inner lines=4Hz); 5.62 (1H, d, J=1 Hz).

EXAMPLE 8Sodium(5R,6S)-6-[(1R)-hydroxyethyl]-2-methylthio-2-formyl-penam-3-carboxylate

Starting from p-nitrobenzyl(5R,6S)-6-[(1R)-tert-butyldimethylsilyloxyethyl]-2-methylthio-2-formylpenam-3-carboxylate, prepared inexample 2, and operating as described in examples 5 and 6, the titlecompound was obtained.

What we claim is:
 1. A lithium, sodium or potassium salt(5R,6S)-6-[(1R)-hydroxyethyl]-2-methylthio-2,2-formylpenam-3-carboxylate.
 2. The sodium salt of the(5R,6S)-6-[(1R)-hydroxyethyl]-2-methylthio-2,2-formylpenam-3-carboxylate of claim
 1. 3. A pharmaceutical compositioncomprising (1) an antibacterially effective amount of a compound ofclaim 1, together with a pharmaceutically acceptable solvent or carrier.4. A pharmaceutical composition comprising (1) an antibacteriallyeffective amount of a compound of claim 2, together with (2) apharmaceutically acceptable solvent or carrier.